1. Field of the Invention
The present invention relates to a tin-nickel alloy and a component surface-treated with such an alloy and, more particularly, to an electronic component to be soldered on a substrate surface with the use of the surface mount technology.
2. Description of Related Art
Typical methods for mounting an electronic component such as a connector on a surface of a substrate include a dip soldering method and a surface mount technology (SMT).
In the dip soldering method, leads and the like of an electronic component are preliminarily inserted into holes formed in a substrate, and the substrate is then dipped in a solder melt in a solder bath. Thus, the solder adheres only onto desired portions to achieve electrical and mechanical connection between the electronic component and the substrate.
In the surface mount technology, a solder paste is preliminarily applied onto electronic component connection areas on a surface of a substrate, and then an electronic component is mounted on the substrate with its joint portions being in contact with the solder paste. Subsequently, the substrate and the electronic component mounted thereon are put in a hot air reflow oven, and maintained in an atmosphere at a peak temperature of about 250.degree. C. for a predetermined period (e.g., 60 seconds to 120 seconds), whereby the solder paste is fused. In turn, the substrate is taken out of the hot air reflow oven and cooled for solidification of the solder paste. Thus, the electrical and mechanical connection between the substrate and the electronic component is achieved.
An electronic component such as a connector which includes a copper alloy base or an iron base, for example, is in some cases subjected to a surface treatment such as plating for improvement of the appearance thereof. In this case, a surface treatment layer (e.g., deposit layer) should have a certain level of solder wettability (particularly, solder wettability after the lapse of a predetermined time from the surface treatment) for easy mounting of the electronic component on a substrate.
Particularly where the surface mount technology is employed, the surface treatment layer should also have a heat resistance sufficient to withstand a treatment at a high temperature.
If the surface treatment layer has an insufficient heat resistance, the layer is melted so that it cannot maintain its good appearance. That is, the surface treatment layer becomes less lustrous, and is roughened or flaked off upon solidification thereof after the melting thereof. The roughening and flaking of the surface treatment layer impair the solderability of the electronic component.
Where an electronic component is mounted on the substrate with the use of the surface mount technology, a palladium deposit layer, which has a higher melting point (1550.degree. C.) and a superior solderability, is conventionally employed as a surface treatment layer.
However, palladium is a very expensive metal, and it is therefore not economical to employ palladium for the formation of a surface treatment layer. Besides palladium, gold and silver are known to have high melting points (1064.4.degree. C. and 961.9.degree. C., respectively) and a satisfactory solderability, but are very expensive. Therefore, gold and silver also have the same drawback as palladium when they are employed for the formation of a surface treatment layer.